1. Field of the Invention
The invention relates generally to a thermal variable-operation regulator and a method for controlling an operating device, and, more specifically, to a thermal variable-operation regulator including an operating device that heats up while operating and a method for controlling such operating device.
2. Description of the Related Art
Thermal variable-operation regulators of the above-mentioned type have been proposed. There are known thermal variable-operation regulators that reduce the maximum operation speed of the motor when the motor load factor exceeds a predetermined threshold value. The thermal variable-operation regulators calculate a motor load factor based on the ratio between a load determination value, which is obtained by integrating the square value of the motor current value proportional to an increase in the temperature of a motor serving as an operating device, and an overload determination value corresponding to the rated load. Such a thermal variable-operation regulator is described, for example, in Japanese Patent Application Publication No. JP-A-09-282020.
The described thermal variable-operation regulator, however, has the following problem. Because the integral value of the square value of the motor current value does not always accurately reflect the temperature of the motor (hereinafter, referred to as the “motor temperature”), the output from the motor is sometimes unnecessarily reduced. In order to address such a problem, the output from the motor may be limited based directly on the motor temperature. However, if the motor temperature rapidly changes, the degree to which the output from the motor is regulated rapidly increases, and, therefore, the output from the motor rapidly changes. As a result, a torque shock occurs, for example, when the motor is used as the drive unit for a vehicle. Alternatively, the output from the motor may be limited using a limitation temperature (that is the temperature based on which the output from the motor is limited), which is obtained by smoothing the motor temperature by using a high time constant so that changes in the motor temperature are more gradual. In this case, even if the detected motor temperature is below the temperature at which the motor would be shut off when the limitation temperature exceeds a shutoff threshold temperature at which the limit value becomes 100%, it takes a long time for the limitation temperature to become lower than the shutoff threshold temperature, because the limitation temperature is obtained by smoothing the motor temperature. As a result, restart of the output from the motor is delayed.